The present invention relates to a connector assembly for coupling a plurality of coaxial cables to a substrate, such as a circuit board, and in particular a connector assembly that provides high RF signal throughput with reduced losses and allows the center contacts of the assembly to be easily serviced or replaced.
The use of RF signals to transfer data among various electronic components has grown in necessity as the complexity of such electronic components has increased. For example, test equipment that is used to analyze semiconductor chips requires very sophisticated data transmission techniques that operate at very high frequencies.
In order to ensure that the high frequency signals are delivered from one piece of equipment to another (e.g., from a test head for a semiconductor chip to a sophisticated piece of analysis equipment), it is common to use flexible or semi-rigid coaxial cable consisting of a center conductor, a dielectric insulator, and an outer shielding conductor. These types of cable are widely available, and can carry signals exceeding 40 GHz.
Since the coaxial cables are repeatedly mated and demated with the associated equipment, it is necessary to use coaxial cable connectors to terminate the ends of the cables, and the connectors must be able to pass the high frequency signals with minimal loss. One example of such a coaxial cable connector is an SSMA type connector, which can easily pass a signal up to 40 GHz.
While the coaxial cable and connectors can transmit high frequency signals, significant losses occur at the juncture between the cable connector and the printed circuit board that forms part of the functional piece of equipment. For example, one type of cable connector includes a connector body that transmits the RF signal in a direction 90 degrees offset from the transmission direction within the coaxial cable. This type of connector is designed to mate with a port that is hard soldered to the circuit board, and the conductor pin in the port also mates with conductive traces on the circuit board at yet another right-angle transition. Accordingly, when using this type of connector, the RF signal must propagate through two right-angle transition points, which results in significant loss to the point where the signal actually delivered to the conductive trace on the circuit board usually cannot exceed 10 GHz.
Another typical cable conductor used in these applications is mounted on the edge of the circuit board, as shown in FIG. 12, in an attempt to avoid the right-angle transitions discussed above (this type of multiple channel connector also allows a plurality of connections with a single coupling operation). This type of xe2x80x9cedge-launchxe2x80x9d connector requires the use of relatively long conductive traces on the circuit board itself to carry the signal to the functional device mounted on the circuit board at some remote location. It is well known, however, that it is very difficult to maintain high RF signals in circuit board conductive traces without experiencing significant losses. RF transmission lines require a delicate balance between the structure and position of the individual copper traces on the circuit board, the spacing therebetween, the ground planes used in the circuit board, and the dielectric materials used to make up the circuit board itself. Standard dielectric materials such as fiber glass materials usually are incapable of maintaining high RF signals within the transmission lines formed on the circuit board. While the dielectric material of the circuit board could be replaced with a higher quality material, this solution unacceptably increases the overall expense of the circuit board.
In order to overcome the inherent shortcomings of transmission lines formed on standard printed circuit boards, it has been a practice to terminate the coaxial cable at a position as close as possible to the intended functional device mounted on the circuit board. This minimizes the length of the conductive trace that must actually be formed on the circuit board. Coaxial connectors that are used for this type of termination are designed to mate with a port extending upwardly from the circuit board. Again, however, there is usually at least one angled transition involved, which, as explained above, results in significant signal loss.
Another problem with attaching the coaxial cable to a position closely adjacent to the intended functional device arises from the fact that the coaxial cable will be subjected to hundreds of mating/demating cycles with the port on the circuit board. Consequently, there is the possibility that the technician performing the connection may damage sensitive electronic components that are positioned adjacent to the port. Still further, when the coaxial cable is semi-rigid, torquing forces imposed on the port by the relatively long coaxial cable can damage the port, the underlying connection to the circuit board, or the circuit board itself, all of which could result in significant repair cost.
Yet another problem with locating the port immediately adjacent to the end device occurs when multiple cables are necessary for communicating with multiple devices on a single circuit board. That is, since each port will be located at a different location on the circuit board, it is impossible to use any type of multiple channel connector (such as shown in FIG. 12), since such a connector would require the ports to be arranged adjacent to one another on the circuit board. Accordingly, whenever a technician has to perform a connection, each of the plurality of coaxial cables has to be handled individually.
Having a plurality of semi-rigid cables connected at a variety of locations on a circuit board gives rise to several additional problems. For example, the more cables a technician has to handle, the more likely it is that there will be a mistake in matching up the correct cable with the correct port. Further, the presence of numerous cables extending in a variety of directions from the circuit board makes it more difficult to access and house the circuit board, especially in test head type applications.
U.S. Pat. No. 4,995,815 attempts to address the problem of remote cable termination at a variety of locations on a circuit board, by providing a coupler that can be mounted directly on the circuit board for electrical connection to a conductive trace formed at some remote location on the circuit board. The coupler disclosed in U.S. ""815 (shown in FIG. 13) also orients the coaxial cable termination end in line with a shorter length of coaxial cable in an attempt to provide a smooth transition onto the circuit board. The above-discussed problems still exist, however, in that the coupler must be positioned at a variety of different locations on the circuit board.
U.S. Pat. No. 6,007,347 also attempts to provide an improved connector assembly for a circuit board. FIG. 14 shows a plurality of coaxial cables 240 extending from a connector frame 140 mounted to the edge of a circuit board 120. The terminal end of each coaxial cable 240 is electrically connected within a complicated xe2x80x9cslot-and-pad connection elementxe2x80x9d 320 formed at specific locations on the circuit board. While this arrangement may be intended to reduce signal loss between the connector at the end of the exterior coaxial cable and the beginning of the conductive trace on the circuit board, it still does not address the inherent problem of signal losses occurring in the conductive traces on the circuit board itself. Specifically, the ""347 patent shows the slot-and-pad connection elements all arranged near the edge of the circuit board, and, consequently, significant signal losses will be encountered within the conductive traces that actually supply the signals to the functional devices that are located at interior, relatively remote portions of the circuit board. In addition, due to the complicated nature of the slot-and-pad connection elements 320, the cost of manufacturing the circuit board is somewhat prohibitive.
In addition to all the above, none of the prior art connector assemblies provides an easy and efficient way to service the assemblies after a predetermined number of mating/demating cycles. That is, in order to maintain high RF throughput through the connector assemblies all the way to the functional devices on the circuit board, the center contacts in the connector assemblies must be periodically replaced. While this may be relatively easy when addressing individual male ports, it becomes a significant problem when dealing with multiple channel connectors, such as shown in FIG. 12. In the event that the center contact of any one connector of the multiple channel connector becomes worn or damaged, and requires replacing, it has been standard practice to simply replace the entire multiple channel connector unit. It would be much more cost effective if the individual center contacts (which are typically the first part to deteriorate) of each conductor could be easily replaced on an as-needed basis.
It is an object of the present invention to overcome the drawbacks of the prior art as discussed above. In accordance with one embodiment of the present invention, a connector assembly for coupling a plurality of coaxial cables to a substrate (e.g., a circuit board) is provided, which includes a housing adapted to be removably attached to a first area of a substrate, the housing having a first wall with an array of holes formed therethrough, and a plurality of connector bodies releasably retained within the housing in substantial alignment with the array of holes. Each connector body includes a bore extending therethrough, an insulator fixed within the bore, and a center contact releasably positioned within a central bore formed in the insulator. A coaxial cable segment is operatively connected to each of the connector bodies, and each coaxial cable segment includes a center conductor fixed to the center contact and an outer shielding conductor fixed to the connector body. Each of the coaxial cable segments extends outwardly from the housing and has a distal end adapted to be connected to another area of the circuit board.
The connector assembly in accordance with the first embodiment of the present invention overcomes many of the drawbacks associated with the prior art. For example, since the connector assembly includes a plurality of coaxial cable segments, the distal end of each coaxial cable segment can be terminated immediately adjacent to any number of functional devices, thus solving the problem of signal losses in the conductive traces on the circuit board.
In addition, since the housing is removably attached to the circuit board, and since the connector bodies are releasably retained within the housing, the connector bodies can be easily accessed for repair and/or replacement with minimal desoldering effort. Moreover, since the center contact is releasably positioned within the central bore of the insulator fixed within the connector body, the center contact can be separated from the connector body with only a single desoldering step. The releasable nature by which the components of the connector assembly are secured to the substrate facilitates long term serviceability of the connector assembly, especially the center contacts, which are typically the first part to deteriorate after repeated mating/demating cycles.
It is preferred that each of the connector bodies has a first end positioned proximate the first wall of the housing and an opposed second end, and is substantially cylindrical having a sidewall defining the bore thereof, and that each of the connector bodies includes a slot extending through the sidewall proximate the second end thereof so that the coaxial cable segment can extend through the slot. This configuration insures a smooth transition for the coaxial cable segment exiting the connector body to help avoid any signal loss in this region. It is also preferred that a plurality of slots are formed through a sidewall of the housing in substantial alignment with the slots in the connector bodies so as to enable the coaxial cables to make a smooth exit from the housing.
To help releasably retain the connector bodies within the housing, it is preferred that each of the connector bodies includes a retaining member proximate the second end thereof, which engages a corresponding portion formed in the housing. More preferably, the retaining member is a radially extending flange and the portion of the housing includes an annular recess that is substantially complementary in shape to and receives the flange. This arrangement allows the connector bodies to be freely positioned on the surface of a circuit board, captured as a group within the housing, and securely, yet releasably, retained within the housing.
In accordance with another embodiment of the present invention, the connector assembly also includes a port fixed to the distal end of each coaxial cable segment to mechanically and electrically terminate the center conductor and the shielding conductor of the coaxial cable segment to the substrate. Preferably, the port has a first section having a first diameter positioned proximate a first end thereof, and a second section having a second diameter positioned proximate a second end thereof, and the shielding conductor of each coaxial cable segment is fixed to the first section and the center conductor extends through the second section.
In accordance with yet another embodiment of the present invention, a circuit board apparatus is provided that includes a circuit board having at least one functional device positioned on a first area thereof and a connector assembly positioned on a second area of the circuit board. The connector assembly includes a housing removably attached to a second area of the circuit board distal from the first area, and the housing includes a first wall with an array of holes formed therethrough, and a plurality of connector bodies releasably retained within the housing in substantial alignment with the array of holes. Each connector body includes a bore extending therethrough, an insulator fixed within the bore, and a center contact releasably positioned within a central bore formed in the insulator. A coaxial cable segment is operatively connected to each of the connector bodies, and each coaxial cable segment includes a center conductor fixed to the center contact and an outer shielding conductor fixed to the connector body. Each of the coaxial cable segments extends outwardly from the housing and has a distal end, and a port is fixed to the distal end of each coaxial cable segment to mechanically and electrically terminate the center conductor and the shielding conductor to the circuit board.
In accordance with still another embodiment of the present invention, a circuit board apparatus is provided that includes a circuit board having at least one functional device positioned on a first area thereof and a connector removably fastened on a second area thereof. The connector includes a substantially cylindrical connector body having a first end, an opposed second end, a sidewall defining a bore extending from the first end to the second end, and a slot extending through the sidewall proximate the second end. An insulator is fixed within the bore and a center contact is releasably positioned within a central bore formed in the insulator. A coaxial cable segment is operatively connected to the connector body and includes a center conductor fixed to the center contact and an outer shielding conductor fixed to the connector body. The coaxial cable segment extends outwardly from the connector body through the slot. A port is fixed to a distal end of the coaxial cable segment to mechanically and electrically terminate the center conductor and the shielding conductor to the circuit board.